The present invention relates to data communications in general and, in particular, to adaptive coding and modulation.
Service providers may desire to use communication systems to provide high availability to high-quality services for their subscribers. Where the network desires to communicate the same or similar information to multiple terminals, however, communications with each terminal may have different characteristics. In certain cases, each terminal may have different and/or changing link conditions (e.g., due to geographic differences in weather, proximity to sources of interference, etc.) In other cases, each terminal may have different capabilities for handling (e.g., receiving, processing, displaying, etc.) information from the network.
These different terminal characteristics may result in differences in apparent availability or quality of services to subscribers. Techniques like adaptive coding and modulation (ACM) may dynamically adjust coding and modulation schemes to adapt to these changing link conditions. For example, as link conditions change, the availability of services may be increased or maintained by using more reliable (lower order) coding and modulation schemes. However, the network may typically send the information at the most reliable modcode to ensure that the terminal with the worst link conditions may still receive the information.
Lower order modulation and coding schemes may use more bandwidth to send error correction data, making them less bandwidth efficient. Because communication systems have limited bandwidth, decreasing bandwidth efficiency may decrease the amount of service-related information that may be transmitted per unit time. This trade-off may mean that service providers will have to choose between providing services with high availability or with high quality.
Thus, there may be a need in the art for new ways to dynamically adjust transmission parameters with an awareness of terminal capabilities to improve both the availability and the quality of network services in differing link conditions.